Compared with glass cups, bone china cups are healthier because the ingredients are natural ingredients.
If the glass is tempered glass, it is not easy to break. The thinner glass is easier to break than bone china. The main reason is that it is not resistant to temperature differences and is easy to explode. Bone china cups are made of animal bone charcoal, clay, feldspar and quartz that use bones as the basic raw materials and are fired twice by high-temperature biscuit firing and low-temperature glaze firing, so they are called bone china cups.
What is the black thing under the bone china cup? If the circle at the bottom is black, you can sand it with sandpaper, and it will fall off. There is no glaze at the bottom, and it is easy to get dirty when it comes into contact with dust. If you can't clean it with water, sand it with sandpaper.
The black spots are the problem of the carcass itself. Dust may have entered during the firing process. If the black spots are under the glaze, they cannot be removed.